1. Field of Invention
The invention generally relates to a synchronization architecture and method for an optical cross connect. More specifically, the invention relates to synchronization architectures and methods particularly well-suited to a SONET/SDH TDM cross connect switch using a CLOS architecture.
2. Description of Related Art
Synchronization is required for SONET/SDH systems. After all, SONET stands for Synchronous Optical Network and SDH stands for Synchronous Digital Hierarchy. In the case of a large scalable switch using a CLOS architecture, the synchronization information must be carried to all the ingress/egress shelves from the center stage shelf. A basic method to pass the synchronization information is to electrically interconnect all the shelves with cables carrying a clock signal and a frame signal as well as a return clock signal used to support the Line Time mode of operation. This approach suffers from the following problems:                Generation of EMI (electromagnetic interference) noise from the high-frequency electrical clock signals being distributed to the shelves        Possible signal integrity issues due to attenuation on long cable interconnects        Connector density issue on the center stage shelf        